How to Picture the Size of the Universe

Space, as Douglas Adams once so aptly wrote, is big.

To try imagining how big, place a penny down in front of you. If our sun were the size of that penny, the nearest star, Alpha Centauri, would be 350 miles away. Depending on where you live, that’s very likely in the next state (or possibly country) over.

Attempting to imagine distances larger than this quickly becomes troublesome. At this scale, the Milky Way galaxy would be 7.5 million miles across, or more than 30 times the distance between the Earth and the moon. As you can see, these are rather inhuman dimensions that are almost impossible to really get a sense of.

But that doesn’t mean it’s completely impossible. Astronomers have made observations and simulations that in some way capture the enormity of our cosmos. In this gallery, Wired will look at the size and scale of the universe’s largest, farthest, and most mysterious objects.

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Size of the Universe

No one knows exactly how large the universe is. It could be infinite or it could have an edge, meaning that traveling for long enough in one direction will bring you back to where you started, like traveling on the surface of a sphere.

Scientists argue over the exact shape and size of the universe but they can calculate one thing with good precision: how far away we can see. Light travels at a specific speed, and because the universe is approximately 13.7 billion years old, we can’t see anything farther away than 13.7 billion light years away, right?

Wrong. The strange thing about space is that it’s expanding. And that expansion can occur at more or less any speed — including faster than light speed — so the most distant objects we can see were in fact once much closer to us. Over time, the universe has shuffled distant stars and galaxies away from us as if they were on an extremely rapid conveyor belt, and dropped them off in far away locations.

Strangely, this means that our observational power is sort of “boosted” and the furthest things we can see are more than 46 billion light years away. While we are not the center of the universe, we are at the center of this observable portion of the universe, which traces out a sphere roughly 93 billion light years across.

It's Full of Galaxies

NASA’s Hubble Space Telescope has produced the deepest image of the universe ever taken. Astronomers generated this picture by pointing Hubble at one small patch of the sky for several months and recording every tiny photon of light they could get. The entire image (below) contains nearly 10,000 galaxies, but here you can see a small sample of what’s out there.

Because looking back in space means we’re also looking back in time, these galaxies are seen as they would have appeared nearly 13 billion years ago, just short of the beginning of time. If you're more spatially inclined, this means that the objects are 30 billion light years away.

But because the universe is ever expanding, and our estimates of its size get more refined over time, astronomers have actually come up with a better way of stating distances. As the universe grows larger, the light waves within it get longer, like a slinky being pulled apart. The wavelength of the light moves toward the redder part of the electromagnetic spectrum, so astronomers talk about the “redshift” of an object, meaning the amount that light waves from that object have expanded since they were emitted.

The galaxies in this image would be more accurately described as being at a redshift of 7.9.

The Most Distant Object Seen

The fuzzy red dot in the center of this image is actually a small galaxy thought to be the most distant object ever seen. Captured by NASA’s Hubble Space Telescope, this galaxy existed just 480 million years after the Big Bang.

The galaxy is estimated to be at a redshift of approximately 10, which is equivalent to a distance of 31.5 billion light years from Earth. The object seems to be a loner, without any other galaxies around it of comparable age. This contrasts with the era 650 million years after the Big Bang, where astronomers have spotted more than 60 galaxies. This suggests that in the cosmic blink of an eye -– merely 200 million years -– larger galaxies built up rapidly from smaller ones.

But astronomers have not entirely confirmed the distance to this object, which means that it could be closer than currently thought. Until NASA launches its next generation telescope, the James Webb Space Telescope, to replace Hubble, astronomers will continue to have scant information about galaxies from this era.

The Farthest Distance

The most distant light that astronomers can see comes from the cosmic microwave background radiation. These are photons that have traveled to us from nearly the beginning of the universe. Shortly after the Big Bang, the universe was too small, and therefore too crowded, for light to travel very far before it was either scattered or absorbed by a particle.

But approximately 380,000 years after the birth of the universe, it became large enough that light could travel freely for the first time without hitting anything. The resulting emission is the limit of what we can see; existing in any direction we point our telescopes. The cosmic microwave background is like a wall that we cannot glimpse beyond.

As the universe expanded, the light within it was stretched out and so this light, which has been traveling for nearly 13.7 billion years, has been lengthened to an enormous degree. The radiation now has a temperature of -455 degrees Fahrenheit, or just slightly warmer than the coldest temperature possible. It is remarkably uniform, with sections differing from one another by only one part in 100,000.

If neutrino detectors are ever built sensitive enough, they might be able to see beyond the cosmic microwave background, to the cosmic neutrino background. Unlike scattering photons, neutrinos pass through ordinary matter with ease, which means they could provide information about the universe from when it was only a few seconds old.

Butterfly of Galaxies

When astronomers look out into the universe, they notice that the objects they see are not distributed willy-nilly. Rather, the force of gravity tends to bring galaxies together into giant agglomerations such as clusters, superclusters, sheets, and walls.

Researchers have scanned the skies and produced incredible maps showing the distribution of the nearest galaxies. While these maps tend to stay within about 7 billion light years from Earth, some surveys have discovered distant quasars -- enormous sources of light from the early universe –- as much as four times that distance.

In the largest survey, the Sloan Digital Sky Survey, astronomers have so far mapped more than one-third of the sky and plotted the location of 500 million individual objects. The image above comes from the 6dF Galaxy Survey, currently the third largest sky survey. The picture has its peculiar shape because astronomers have to aim their telescopes away from the bright light of the Milky Way galaxy, which obscures the sections of the sky in the center of the image.

Nearby Superclusters

Close to home, astronomers have a relatively good idea of what our immediate cosmic neighborhood looks like. Within about a billion light years of Earth, we see a sea of superclusters. These are groups of groups of galaxies that are strung together under the influence of gravity.

The Milky Way galaxy is part of the Virgo Supercluster, seen at the center of this image. Our home galaxy is actually nothing but a side character in this group, which is dominated by the massive Virgo Cluster, made up of more than 1,300 galaxies 54 million light years away.

The Coma Supercluster is interesting to note because it sits at the center of the Northern Great Wall, a staggeringly enormous filament of galaxies 500 million light years across and 300 million light years wide. The largest supercluster in our vicinity is the Horologium Supercluster, which stretches across half a billion light years.

Dark Matter and Energy

Invisible in all this large-scale grandeur is the stuff we can’t see. Dark matter is a mysterious invisible substance that is thought to pervade the universe, interacting gravitationally with ordinary matter but shying away from light and other electromagnetic forces.

How do we know the dark matter is there if we can’t see it? Because it still manages to make its presence felt. For instance, our local supercluster, the Virgo Supercluster, has an estimated total mass 1015 times the mass of the sun (that’s one quadrillion, for those who like names for their numbers). But the supercluster’s luminosity is only about three trillion times that of the sun. This means that the Virgo Supercluster is 300 times less bright than it should be given its mass, suggesting the presence of a great amount matter sitting idly around and not producing any light, hence “dark matter.”

While dark matter in the universe is thought to outweigh ordinary matter by a ratio of five to one, both are severely overpowered by dark energy –- a strange force driving the accelerated expansion of the universe. Despite being the subject of the most recent Nobel Prize in Physics, researchers are still at a loss to explain what dark energy is. The description currently serves as a sort of placeholder until more accurate theories are developed to explain its presence.

Image: NASA/WMAP Science Team

The Cosmic Web

Galactic surveys have revealed that the universe has a “bubbly texture.” Almost all galaxies are found within giant arcs surrounding enormous voids, some more than 300 million light years across, containing little other than empty space. Though it can’t be seen, dark matter dominates most of the structure.

As seen in the simulation above, the universe is arranged into great collections of knots, sheets, and filaments. These formations got their start from the tiny fluctuations in the cosmic background radiation, which represent areas of slightly more or less density. As the universe evolved, these small inhomogeneities attracted matter to them, which snowballed over billions of years into the enormous collections we now see.

Massive Model

In 2005, an international group of researchers wanted to see if our current understanding about the universe works. They produced the “Millennium Run,” a simulation of more than 10 billion particles running around and interacting in a cube 2 billion light years on each side.

The model, which incorporates ordinary matter as well as dark matter and dark energy, shows how the large-scale structure of the universe arises from known physics. Over the course of this simulated universe’s history, the researchers witnessed the formation of model supermassive black holes, powerful quasars spewing out radiation, and roughly 20 million galaxies.

The researchers found that their simulated observations corresponded quite closely to the real cosmos, producing the beautiful image seen above. The white line indicates the scale, which is 125 megaparsecs, or more than 400 million light years across (the h stands for the Hubble parameter, a number that represents astronomer’s uncertainty regarding distance, and which is currently calculated to be 0.72.)